Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.28   3.724%   $212.9246   $212.92   $212.90   $212.90  
  Purchase #2 $61.33   4.414%   $64.0371   $64.04   $64.05   $64.00  
  Purchase #3 $75.80   3.439%   $78.4068   $78.41   $78.40   $78.40  
  Purchase #4 $213.48   11.130%   $237.2403   $237.24   $237.25   $237.20  
  Purchase #5 $119.41   13.510%   $135.5423   $135.54   $135.55   $135.50  
  Purchase #6 $236.54   7.485%   $254.245   $254.25   $254.25   $254.20  
  Purchase #7 $62.29   3.287%   $64.3375   $64.34   $64.35   $64.30  
  7 purchase totals = $974.13       $1,046.7336   $1,046.74   $1,046.75   $1,046.50